I would like to run postfix as my MTA using MySQL as backend. Unfortunately the official package repo only offers sendmail, no postfix so I wonder which is the best source for postfix on OpenSolaris. I don't like installing non-packaged software.

Should I use

blastwave

opencsw

use spec files from SFE to compile it myself

or build my own packages from scratch?

Additionally: anything I have to mind which is special to OpenSolaris in regards to postfix?

Rolling your own from source isn't a bad thing per se; Even in situations where you have a packaged version that integrates into your package management system. You might want to apply some patches from the mailing list, link it to special versions of some of the dependency libraries (think non-GNU version, system libraries, blastwave libs, etc.). You're more flexible by using the source.